2、 如果当客户端还有一个打开的套接字，而服务端此时却关闭了，会发生什么呢？反之呢？
3、 试着运行一个服务端和两个客户端。我们前面说过，服务端只能处理一个客户端，为使服务端能同时处理多个客户端，需要进行多线程设计，建议对服务端作一些适当的修改，并用两个、三个、或更多客户端来测试。
4、 以下是当有两个客户端运行时的输出：
Client 2600 4
Sent values 56 and 35, received result 91
Sent values 48 and 20, received result 68
Sent values 6 and 97, received result 103
Sent values 76 and 9, received result 85
Notified server we're shutting down
Shutting down client
Client 2600 2
Sent values 69 and 66, received result 135
Sent values 84 and 45, received result 129
Notified server we're shutting down
Shutting down client
Server 2600
Waiting for new connection request
New connection accepted
Started thread Thread-1
Waiting for new connection request
Executing thread Thread-1
Received values 56 and 35, sent result 91
New connection accepted
Started thread Thread-2
Waiting for new connection request
Executing thread Thread-2
Received values 69 and 66, sent result 135
Received values 48 and 20, sent result 68
Received values 84 and 45, sent result 129
Received values 6 and 97, sent result 103
Shutting down server thread Thread-2
Received values 76 and 9, sent result 85
Shutting down server thread Thread-1
